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Wednesday, August 26, 2015

25 Best MySQL DATABASE interview questions

How do you start MySQL on Linux?- /etc/init.d/mysql start

How do you start and stop MySQL on Windows?net start MySQL, net stop MySQLWhat’s the default port for MySQL Server?3306What does tee command do in MySQL? tee followed by a filename turns on MySQL logging to a specified file. It can be stopped by command notee.Can you save your connection settings to a conf file?Yes,
and name it ~/.my.conf. You might want to change the permissions on the
file to 600, so that it’s not readable by others.Have you ever used MySQL Administrator and MySQL Query Browser? Describe the tasks you accomplished with these tools.What are some good ideas regarding user security in MySQL?There is no user without a password. There is no user without a user
name. There is no user whose Host column contains % (which here
indicates that the user can log in from anywhere in the network or the
Internet). There are as few users as possible (in the ideal case only
root) who have unrestricted access.How do you change a password for an existing user via mysqladmin?mysqladmin -u root -p password "newpassword" Explain the difference between MyISAM Static and MyISAM Dynamic.In MyISAM static all the fields have fixed width. The Dynamic MyISAM
table would include fields such as TEXT, BLOB, etc. to accommodate the
data types with various lengths. MyISAM Static would be easier to
restore in case of corruption, since even though you might lose some
data, you know exactly where to look for the beginning of the next
record.What does myisamchk do?It compressed the MyISAM tables, which reduces their disk usage.Explain advantages of InnoDB over MyISAM?Row-level locking, transactions, foreign key constraints and crash recovery.Explain advantages of MyISAM over InnoDB?Much more
conservative approach to disk space management - each MyISAM table is
stored in a separate file, which could be compressed then with myisamchk
if needed. With InnoDB the tables are stored in tablespace, and not
much further optimization is possible. All data except for TEXT and BLOB
can occupy 8,000 bytes at most. No full text indexing is available for
InnoDB. TRhe COUNT(*)s execute slower than in MyISAM due to tablespace
complexity.What are HEAP tables in MySQL?HEAP tables are in-memory.
They are usually used for high-speed temporary storage. No TEXT or BLOB
fields are allowed within HEAP tables. You can only use the comparison
operators = and <=>. HEAP tables do not support AUTO_INCREMENT.
Indexes must be NOT NULL.How do you control the max size of a HEAP table?MySQL config variable max_heap_table_size.Explain the difference between mysql and mysqli interfaces in PHP?mysqli is the object-oriented version of mysql library functions.What are CSV tables?Those are the special tables, data for which is saved into comma-separated values files. They cannot be indexed.Explain federated tables. - Introduced in MySQL 5.0, federated tables allow access to the tables located on other databases on other servers.What is SERIAL data type in MySQL?BIGINT NOT NULL PRIMARY KEY AUTO_INCREMENTWhat happens when the column is set to AUTO INCREMENT and you reach the maximum value for that table?It stops incrementing. It does not overflow to 0 to prevent data
losses, but further inserts are going to produce an error, since the key
has been used already.Explain the difference between FLOAT, DOUBLE and REAL.FLOATs store floating point numbers with 8 place accuracy and take up 4
bytes. DOUBLEs store floating point numbers with 16 place accuracy and
take up 8 bytes. REAL is a synonym of FLOAT for now.If you specify the data type as DECIMAL (5,2), what’s the range of values that can go in this table? - 999.99 to -99.99. Note that with the negative number the minus sign is considered one of the digits.Use mysqldump to create a copy of the database? mysqldump -h mysqlhost -u username -p mydatabasename > dbdump.sql What happens if a table has one column defined as TIMESTAMP?That field gets the current timestamp whenever the row gets altered.But what if you really want to store the timestamp data, such as the publication date of the article? Create two columns of type TIMESTAMP and use the second one for your real data.Explain the difference between BOOL, TINYINT and BIT.Prior
to MySQL 5.0.3: those are all synonyms. After MySQL 5.0.3: BIT data
type can store 8 bytes of data and should be used for binary data.

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